feat: Added GPU support for classification and improve memory pinning

[fg-mindee]

This PR introduces the following modifications:

• removes unnecessary metric reset (it's already done at the beginning of evaluate)
• added missing support of GPU for character classification in PyTorch
• improved memory pinning for CPU training (if "True" it preallocates the memory on GPU, but in case of CPU training, we don't want that)

Any feedback is welcome!

[charlesmindee]

Thanks!

[codecov]

Codecov Report

Merging #629 (e7f10f6) into main (fc22516) will increase coverage by 0.02%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #629      +/-   ##
==========================================
+ Coverage   96.05%   96.07%   +0.02%     
==========================================
  Files         112      112              
  Lines        4359     4359              
==========================================
+ Hits         4187     4188       +1     
+ Misses        172      171       -1     

Flag	Coverage Δ
unittests	96.07% <ø> (+0.02%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...dels/detection/differentiable_binarization/base.py	91.82% <0.00%> (+0.62%)	⬆️

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